JP2002300005A - Surface acoustic wave filter device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface acoustic wave filter device with a balance- unbalance conversion function, the input impedance of which is equal to the output impedance that can extend an out pass-band attenuation. SOLUTION: The surface acoustic wave filter device with an unbalance signal terminal 231 and 1st, 2nd balance signal terminals 212, 227, and the input impedance of which is equal to the output impedance, is provided with 1st, 2nd surface acoustic wave filters 201, 216 the input or output impedance of which is about a multiple of four of the output or input impedance. That is, 2<n-1> (n is an integer of 1 or over) sets of the 1st surface acoustic wave filters 201 are connected between the unbalance signal terminal 231 and the 1st balance signal terminal 212 and 2<n-1> sets of the 2nd surface acoustic wave filter 216 whose phase differs from that of the filters 201 by 180 degrees are connected between the unbalance signal terminal 231 and the 2nd balance signal terminal 216 are connected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave filter device used as a bandpass filter in, for example, a portable telephone, and more particularly, to a surface acoustic wave filter having a balanced-unbalanced conversion function and having substantially equal input and output impedances. Related to the device.

[0002]

2. Description of the Related Art In recent years, with the miniaturization and weight reduction of mobile phones, not only the number of components constituting the mobile phone has been reduced and the size of the components has been reduced, but also a composite component obtained by combining a plurality of functions. Development is progressing. Under such circumstances, as a surface acoustic wave filter used in the RF stage of a mobile phone, a surface acoustic wave filter device having a balanced-unbalanced conversion function, a so-called balun function, has been actively studied. It has been used for GSM mobile phones and the like.

For example, Japanese Patent Application Laid-Open No. 9-205342 discloses a surface acoustic wave filter device having such a balanced-unbalanced conversion function. FIG. 18 is a schematic plan view showing an electrode structure of an example of a longitudinally coupled resonator type surface acoustic wave filter device having a conventional balanced-unbalanced conversion function. The surface acoustic wave filter device 100 has substantially the same input / output impedance and has a balance-unbalance conversion function. On the piezoelectric substrate, three I
DTs 102 to 104 are arranged, and IDTs 102 to 104 are provided.
The reflectors 101 and 105 are arranged outside the area where the 104 is provided in the surface wave propagation direction. IDT102,
104 are connected in common and connected to an unbalanced signal terminal 106. Both ends of the IDT 103 are connected to first and second balanced signal terminals 107 and 108, respectively.

[0004]

SUMMARY OF THE INVENTION In a filter having a balanced-unbalanced conversion function, transmission characteristics in a pass band between an unbalanced signal terminal and a first balanced signal terminal, and a filter having an unbalanced signal terminal and a second balanced signal terminal. , It is required that the amplitude characteristics are equal and the phase is different by 180 degrees in the pass band between them and the balanced signal terminal, and that the amplitude characteristics and the phase characteristics are equal outside the pass band.

[0005] The amplitude balance and the phase balance are defined as a three-port device in which a filter having a balance-unbalance conversion function is used. For example, an unbalanced input terminal is port 1 and a first and a second balanced output terminal are respectively connected. When port 2 and port 3 are used, they are expressed as follows.

Amplitude balance = | A |, where A = | 20 l
ogS21 | − | 20logS31 | phase balance = | B−180 |, where B = | ∠S21−
∠S31 | Note that S21 indicates a transfer coefficient from the first port to the second port, and S31 indicates a transfer coefficient from the first port to the third port. A shows the difference between the decibel value of S21 and the decibel value of S31.

Ideally, the amplitude balance is 0 dB and the phase balance is 0 degree within the pass band of the filter, and the amplitude balance is 0 dB and the phase balance is 1 outside the pass band.
80 degrees.

However, the conventional surface acoustic wave filter device 100 shown in FIG. 18 has a problem that the degree of balance does not reach the ideal degree of balance and is not sufficient. This is because the balanced signal terminal 107 has an IDT 103 and IDTs on both sides.
Since a bridging capacitance is added to the balanced signal terminals 102 and 104, and a capacitance is inserted between the balanced signal terminal 108 and the ground potential, the parasitic capacitance differs between the balanced signal terminals 107 and 108. is there. Therefore, there is a problem that the difference in the parasitic capacitance deteriorates the balance, particularly the balance outside the pass band, and reduces the out-of-band attenuation.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks of the prior art, and in a surface acoustic wave filter device having a balance-unbalance conversion function, the degree of balance outside the pass band is improved and the attenuation outside the pass band is reduced. It is an object of the present invention to provide a surface acoustic wave filter device having a structure capable of suppressing the reduction and a communication device having the surface acoustic wave filter.

[0010]

According to the present invention, there is provided a surface acoustic wave filter device having an unbalanced signal terminal, first and second balanced signal terminals, and having substantially equal input and output impedances. 2 ^{n -1} (where n is an integer of 1 or more) first input terminals connected between the signal terminal and the first balanced signal terminal, and one of the input and output impedances is about four times the other. A surface acoustic wave filter, the first surface acoustic wave filter being connected between the unbalanced signal terminal and the second balanced signal terminal, wherein one of input and output impedances is about four times as large as the other. 2 ^n-1 (n
Is an integer of 1 or more) second surface acoustic wave filters.

In a first specific aspect of the present invention, the first and second surface acoustic wave filters have one or more IDTs arranged along a surface acoustic wave propagation direction, Has at least one IDT portion divided into two in the cross width direction, and the first and second IDT portions are connected in series.

In a more specific aspect of the present invention, the first and second surface acoustic wave filters each include at least one IDT in a virtual surface acoustic wave filter configured such that input and output impedances are substantially equal. It has a structure in which the first and second IDT sections are divided into two in the cross width direction.

As the virtual surface acoustic wave filter,
In a specific aspect of the present invention, a longitudinally coupled resonator type surface acoustic wave filter is used. In a more specific aspect of the present invention, the longitudinally coupled resonator type surface acoustic wave filter has three IDTs arranged in the direction of propagation of the surface acoustic wave, and the center IDT or the IDTs on both sides are arranged in the cross width direction. To form the first and second IDT sections.

In a second specific aspect of the present invention, the first and second surface acoustic wave filters each include one or more I
First and second IDTs each having a DT and configured by dividing at least one IDT into two in a surface wave propagation direction.
Having a part.

[0015] In a more limited example of the second specific aspect of the present invention, the first and second surface acoustic wave filters are arranged so that input and output impedances are substantially equal. The filter is configured by dividing at least one IDT into two in the surface wave propagation direction. The virtual surface acoustic wave filter is not particularly limited, but a longitudinally coupled resonator type surface acoustic wave filter is preferably used.

In a more limited aspect of the second aspect of the present invention, the virtual longitudinally coupled resonator type surface acoustic wave filter has three IDTs, and the central IDT has a surface wave propagation direction. Are divided into two.

In the first and second aspects of the present invention, preferably, one of the first and second IDT units is connected to the ground potential, thereby connecting the SAW filter between the balanced and unbalanced terminals. One of the output impedances is about four times the other.

In a third specific aspect of the present invention, the first and second surface acoustic wave filters have a structure in which at least two IDTs are connected in series in a surface acoustic wave filter having a plurality of IDTs.

In a specific example of the third aspect, the first and second surface acoustic wave filters have a structure in which at least two IDTs are connected in series in a virtual surface acoustic wave filter having substantially the same input / output impedance. Having. As the virtual surface acoustic wave filter, a longitudinally coupled resonator type surface acoustic wave filter is preferably used.

In a more specific example of the third aspect of the present invention, the virtual longitudinally coupled resonator type surface acoustic wave filter includes:
It has three IDTs, and the IDTs on both sides in the surface wave propagation direction are connected in series.

A communication device according to the present invention is characterized in that a surface acoustic wave filter device constructed according to the present invention is provided as a bandpass filter.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.

FIG. 1 is a schematic plan view for explaining a surface acoustic wave filter device according to a first embodiment of the present invention. The surface acoustic wave filter device according to the present embodiment is used as a DCS receiving filter having a pass band of 1 to 3 GHz.

In this embodiment, a surface acoustic wave filter device is formed by forming the electrode structure shown in FIG. 1 on a YcutX-propagating LiTaO ₃ substrate (not shown) of 40 ± 5 degrees.

The surface acoustic wave filter device 200 has a first surface acoustic wave filter 201, and a second surface acoustic wave filter 216 having a phase 180 degrees different from that of the first surface acoustic wave filter.

The first surface acoustic wave filter 201 has IDTs 203 to 205 arranged along the surface acoustic wave propagation direction. Reflectors 202 and 206 are arranged on both sides of the region where the IDTs 203 to 205 are provided in the surface wave propagation direction.

The IDT 203 has IDT sections 203A and 203B divided into two in the direction orthogonal to the surface wave propagation direction. Similarly, the IDT 205 has IDT units 205A and 205B divided into two in a direction orthogonal to the surface acoustic wave propagation direction. The IDT units 203A and 203B are connected in series. Similarly, the IDT units 205A and 205B are connected in series.

The IDT unit 203A of the IDT 203
The terminal 21 is commonly connected to the IDT unit 205A of
5 is connected. Terminal 215 is the unbalanced signal terminal 2
31. Also, the IDT units 203A, 203A
The end opposite to the side connected to the unbalanced signal terminal 231 of 5A is connected to the IDT units 203B and 205B, and the other ends of the IDT units 203B and 205B are connected to the ground potential.

One end of the center IDT 204 is connected to the ground potential, and the other end is connected to the first balanced signal terminal 212. In the surface acoustic wave filter 201, the impedance at the terminal 215 is
Is about four times the impedance at.

The surface acoustic wave filter 201 is a virtual longitudinally coupled resonator type surface acoustic wave filter 30 shown in FIG.
0 corresponds to a modified version. That is, the surface acoustic wave filter 300 is designed so that the input and output impedances are substantially equal, and has three IDTs 302 to 304 arranged along the propagation direction of the surface acoustic wave. Note that 30
Reference numeral 1305 denotes a reflector. This surface acoustic wave filter 3
At 00, the IDTs 302 and 304 on both sides are divided in the direction orthogonal to the surface wave propagation direction so as to have the first and second IDT portions as described above, and the first and second IDT portions are connected in series. Thus, the surface acoustic wave filter 201
, Whereby the impedance at the terminal 215 is about four times the impedance at the balanced signal terminal 212.

The second surface acoustic wave filter 216 has the same configuration as that of the first surface acoustic wave filter 201 except that the polarity of the central IDT 220 is inverted. That is, the reflectors 217 and 222 are
02, 206, and the two divided I
The IDTs 219 and 221 having the DT units 219A, 219B, 221A and 221B have the same configuration as the IDTs 203 and 205.

As described above, the polarity of the IDT 220 is I
Since the polarity of the surface acoustic wave filter 216 is inverted with respect to the polarity of the DT 204,
One phase differs by 180 degrees.

IDT of second surface acoustic wave filter 216
Parts 219A and 221A are commonly connected to terminal 230. The terminal 230 is connected to the unbalanced signal terminal 231. 219B of IDT part of IDT219,221,
221B are each connected to the ground potential.
One end of the IDT 220 is connected to the ground potential, and the other end is connected to the second balanced signal terminal 227.

In this embodiment, the IDT 204 at the center of the first surface acoustic wave filter 201 is connected to the first balanced signal terminal 21.
2, the central IDT 220 of the second surface acoustic wave filter 216 is connected to the second balanced signal terminal 227, and the terminals 215 and 230 are connected to the unbalanced signal terminal 231. SAW filter device 2 having equal and balanced-unbalanced conversion function
00 is configured. In FIG. 1, for simplicity, the IDT and the reflector are shown schematically, and the number of electrode fingers is different from the actual number.

Next, specific characteristics of the surface acoustic wave filter device of this embodiment will be described based on experimental examples. For comparison, a virtual longitudinally coupled resonator type surface acoustic wave filter shown in FIG. 2 was prepared as a conventional example. The details of the design of the longitudinally coupled resonator type surface acoustic wave filter 300 are as follows.

Electrode finger cross width W: 74.8λI (where λ
I is the wavelength of the IDT) The number of electrode fingers of the IDT (IDTs 302, 303, 304)
): 23, 33, 23 IDT wavelength λI: 2.14 μm Reflector wavelength λR: 2.19 μm Number of reflector electrode fingers: 150 IDT-IDT interval (between adjacent electrode finger centers) distance):
0.32λI Distance between IDT and reflector (distance between centers of adjacent electrode fingers): 0.53λI Duty in IDT: 0.63 Duty in reflector: 0.57 Film thickness of electrode finger: 0.088λI As described above. In the conventional surface acoustic wave filter device 300 designed as described above, the IDTs 302 and 304 are commonly connected, connected to the unbalanced signal terminal 313, and both ends of the IDT 303 are defined as first and second balanced signal terminals 308 and 309. ,
The properties were measured.

A surface acoustic wave filter device 200 was designed under the same conditions as those of the longitudinally coupled resonator type surface acoustic wave filter 300 as a conventional example prepared as described above. However, as described above, the surface acoustic wave filters 201, 21
6, the IDTs 203, 205, 219, 221
Was divided into two in the direction orthogonal to the surface wave propagation direction. Also,
The polarity of the IDT 220 is inverted from that of the IDT 204.
In the surface acoustic wave filter device 200 of the embodiment, the electrode finger cross width W was set to 37λI. This is to make the input and output impedances of the embodiment and the conventional example equal. In other respects, the surface acoustic wave filter device 200 of the embodiment was configured in the same manner as the above-described conventional example.

FIG. 3 is a diagram showing the amplitude balance of the surface acoustic wave filter devices of the conventional example and the first embodiment.
FIG. 5 is a diagram showing a phase balance degree, and FIG. 5 is a diagram showing an attenuation frequency characteristic. 3 to 5, the characteristic of the conventional example is indicated by a broken line, and the characteristic of the embodiment is indicated by a solid line.

As is apparent from the amplitude balance in FIG. 3, in the conventional example, the amplitude balance greatly changes from around 3 GHz to around 6 GHz, and exceeds 10 dB at around 5 GHz. On the other hand, in the present embodiment, 3 GHz to 6 G
Within the Hz band, the amplitude balance is suppressed to within approximately 1 dB. In addition, it is understood that the amplitude balance is improved according to the embodiment even in a frequency region of 1 GHz or less.

The same applies to the phase balance shown in FIG. 4. In the conventional example, the phase balance greatly changes from about 3 GHz to about 6 GHz, and changes from 0 degrees to 180 degrees. On the other hand, in the present embodiment, the phase balance in this band is substantially in the range of 170 to 180 degrees. It can also be seen that, even in the frequency range of 1 GHz or less, the degree of phase balance is greatly improved according to the embodiment.

As described above, in the frequency region outside the pass band (1 to 3 GHz), according to the embodiment, the amplitude balance approaches 0 dB and the phase balance approaches 180 degrees.
As shown in FIG. 5, it can be seen that the attenuation outside the passband is greatly improved. In comparison with the conventional example, according to the embodiment, the attenuation amount is 10 dB in the frequency region of 1 GHz or less.
Improved, at least 1 in the frequency range above 3 GHz
It can be seen that it is improved by 5 dB, especially by around 40 dB near 4.5 GHz.

As described above, in the surface acoustic wave filter device 200 of the present embodiment, the reason why the degree of balance is improved and the attenuation outside the pass band is improved is considered as follows.

In the conventional example of FIG. 2, the balanced signal terminals 308,
309, the parasitic capacitance is different. That is, the parasitic capacitance applied to the balanced signal terminal 309 is mainly due to the central ID
The parasitic capacitance added to the balanced signal terminal 308 is mainly a capacitance inserted between the T303 and the left and right IDTs 302 and 304, while the parasitic capacitance is applied to the ground signal. It is considered that due to the difference due to the influence of the parasitic capacitance, the degree of balance, particularly the degree of balance outside the pass band, has deteriorated, and the attenuation has been reduced.

On the other hand, in the present embodiment, the first and second
Since the ground potential exists around the balanced signal terminals 212 and 227, the parasitic capacitance applied to any of the balanced signal terminals is mainly a capacitance inserted between the ground signal and the first and second balanced signal terminals. The equivalent parasitic capacitance is added to the balanced signal terminals 212 and 227. Therefore, since the difference in the parasitic capacitance applied to the balanced signal terminals 212 and 227 is small, the amplitude balance outside the band approaches 0 dB, and the phase balance approaches 180 degrees, whereby the attenuation outside the pass band is greatly improved. It is thought that there is.

In the first embodiment, the surface acoustic wave filter device 200 is constituted by using two 3IDT type longitudinally coupled resonator type surface acoustic wave filters. However, as shown in FIG. 1, second surface acoustic wave filters 701, 70
2, the first and second surface acoustic wave filters 703 and 704 may be connected in parallel. The first and second surface acoustic wave filters 701 and 702 are configured in the same manner as the surface acoustic wave filters 201 and 216 of the above-described embodiments, and the surface acoustic wave filters 703 and 704 are also configured as surface acoustic wave filters 201 and 216. It is configured similarly to.

The surface acoustic wave filters 701 and 702
And one end of each of the surface acoustic wave filters 703 and 704 are commonly connected to an unbalanced signal terminal 705. First and second balanced signal terminals 706 and 707
Are connected to the central IDT of the surface acoustic wave filters 701 and 703 and the surface acoustic wave filters 702 and 704, respectively. As described above, even in the structure using the four-element surface acoustic wave filter, the out-of-passband attenuation can be similarly improved by configuring in the same manner as in the above embodiment.

Further, in the present invention, the number of IDTs of the first and second surface acoustic wave filters is not limited to three. For example, as in the modification shown in FIG. 7, the first surface acoustic wave filter 201A and the second surface acoustic wave
16A may have two IDTs. The first surface acoustic wave filter 201A includes:
The second surface acoustic wave filter 216A corresponds to a structure obtained by removing the IDT 203 from the surface acoustic wave filter 201.
This corresponds to a structure in which IDT 221 is removed from second surface acoustic wave filter 216. However, the interval between the reflector and the IDT is configured in the same manner as in the above embodiment.

Therefore, one ends of the IDTs 204 and 220 are connected to the first and second balanced signal terminals 212 and 227, and one ends of the IDTs 205 and 219 are connected to the unbalanced signal terminals 23.
1 connected.

As shown in FIG. 8, a 5-IDT type surface acoustic wave filter may be used as each of the first and second surface acoustic wave filters 201B and 216B.
Here, the surface acoustic wave filter 201B has the same configuration as the surface acoustic wave filter 201, except that the IDTs 251 and 252 are further arranged on both sides of the IDTs 203 and 205 in the surface wave propagation direction. The IDTs 253 and 25 are also used for the second surface acoustic wave filter 216B.
The configuration is the same as that of the second surface acoustic wave filter 216 except that the fourth surface acoustic wave 4 is disposed outside the IDTs 219 and 221 in the surface wave propagation direction.

Also in the surface acoustic wave filter device of each of the modifications shown in FIGS. 7 and 8, the first surface acoustic wave filter in which one of the input and output impedances is four times the other is used as the first surface acoustic wave filter. A filter and 2 ^n-1 second surface acoustic wave filters each having one input / output impedance four times as large as the other and having a phase 180 degrees different from the first surface acoustic wave filter (where n Is an integer of 1 or more)
By connecting the surface acoustic wave filters in which the total number of the first and second surface acoustic wave filters is 2 ^{n in the same} manner as in the above embodiment, the amount of attenuation outside the pass band is similarly increased. be able to. In order to obtain a desired frequency characteristic, the electrode finger crossing width, the number of IDTs, and the like may be adjusted as needed, and a trap may be added as needed.

FIG. 9 is a schematic plan view showing an electrode structure of a surface acoustic wave filter device according to a second embodiment of the present invention. Also in this embodiment, a surface acoustic wave filter device used as a DCS receiving filter having a pass band of 1 to 3 GHz is configured.

An electrode structure shown in FIG. 9 is formed on a YcutX propagation LiTaO ₃ substrate (not shown) at 40 ± 5 degrees. In the surface acoustic wave filter device 800, the first and second
, And the first and second surface acoustic wave filters 803 and 804 are used. That is, a surface acoustic wave filter device having a four-element structure is configured.

This surface acoustic wave filter device 800 is constructed by connecting two stages of the surface acoustic wave filter device 1100 of the modification shown in FIG. 10 in parallel. For ease of explanation, the structure of the surface acoustic wave filter device 1100 shown in FIG. 10 will be described first. The surface acoustic wave filter device 1100 includes a first surface acoustic wave filter 1101 and a second surface acoustic wave filter 1115 whose phase is different from that of the first surface acoustic wave filter 1101 by 180 degrees.

The first surface acoustic wave filter 1101 is a virtual longitudinally coupled resonator type surface acoustic wave filter having substantially equal input and output impedances and three IDTs. It has a divided structure. That is, the central IDT 1104 is divided into two, and the IDT units 1104A and 1104B are configured. IDT11 on both sides of IDT1104 in the direction of surface wave propagation.
03, 1105, and IDT 1103, 1
The reflectors 1102 and 1106 are arranged outside the region where the 104 and 1105 are formed in the propagation direction of the surface acoustic wave.

One end of one of the IDT sections 1104A and 1104B is connected to the ground potential, and the other end of the IDT section 1104A and the IDT 1104A are connected to the ground potential.
One end of B is shared, and the other end of IDT 1104B is connected to unbalanced signal terminal 1129. Also,
One end of each of the IDTs 1103 and 1105 is connected to the ground potential, and the other end is commonly connected to the first balanced signal terminal 1114.

Similarly, the second surface acoustic wave filter 111
Also in 5, the first IDT 1118A and the second IDT 1118B are configured by dividing the central IDT 1118 in the same manner in the surface wave propagation direction. One end of the IDT unit 1118B is connected to the ground potential,
One end of the T section 1118A is connected to the unbalanced signal terminal 1129. Further, one ends of the IDTs 1117 and 1119 are connected to the ground potential, and the other ends are commonly connected and connected to the second balanced signal terminal 1128. 1
Reference numerals 116 and 1120 denote reflectors.

One end of the IDT 1104A is connected to the ground potential, and the other end of the IDT 1104B is connected to the unbalanced signal terminal 11.
29, the surface acoustic wave filter 110
In 1, the impedance of the terminal 1129 is four times the impedance of the terminal 1114. Similarly, in the surface acoustic wave filter 1115, the impedance of the terminal 1129 is different from the impedance of the terminal 1128.

On the other hand, between the unbalanced signal terminal 1129 and the first and second balanced signal terminals 1114 and 1128, the first and second surface acoustic wave filters 1101 and 111
5 is connected as described above, it is possible to increase the amount of attenuation outside the pass band as in the first embodiment.

Next, the surface acoustic wave filter device 800 according to the second embodiment shown in FIG. 9 will be described. The surface acoustic wave filter device 800 corresponds to a structure in which two surface acoustic wave filter devices 1100 having the first and second surface acoustic wave filters 1101 and 1115 are connected in parallel. That is, similarly to the surface acoustic wave filter 1101, the surface acoustic wave filters 801 and 803 are used.
2, 804 are configured similarly to the surface acoustic wave filter 1115.

The surface acoustic wave filter device 800 of the second embodiment shown in FIG. 9 was designed under the same conditions as in the first embodiment, and the characteristics were measured. The results are shown by solid lines in FIGS. For comparison, the characteristics of the conventional example shown in FIG. 2 are shown by broken lines in FIGS.

As is clear from FIGS. 11 to 13, the parasitic capacitance applied to the first and second balanced signal terminals in this embodiment is also substantially equal, so that the amplitude balance outside the pass band is smaller than in the conventional example. And the degree of phase balance can be improved. That is, as shown in FIG. 11, according to the present embodiment, the amplitude balance degree approaches 0 dB outside the pass band (the band below 1 GHz and the band above 3 GHz), and FIG.
As is apparent from FIG. 2, the phase balance approaches 180 degrees.
Accordingly, as shown in FIG. 13, the out-of-band attenuation is greatly improved.

The same effect as in the second embodiment can be obtained in the surface acoustic wave filter device 1100 having a two-element configuration shown in FIG. Further, the input impedance or output impedance is not limited to the four-element surface acoustic wave filter device 800 or the two-element surface acoustic wave filter device 1100 as in the above embodiment, and is four times as large as the output impedance or the input impedance. A first surface acoustic wave filter having a phase difference of 180 degrees;
As long as 2 ^n-1 (n is an integer of 1 or more) surface acoustic wave filters are connected, the same effect as in the above embodiment can be obtained.

FIG. 14 is a schematic plan view showing the electrode structure of the surface acoustic wave filter device according to the third embodiment. Also in the present embodiment, DC having a pass band of 1 to 3 GHz is used.
A surface acoustic wave filter device as an S receiving filter is configured.

An electrode structure shown in FIG. 14 is formed on a 40 ± 5 ° YcutX-propagating LiTaO ₃ substrate (not shown), and a surface acoustic wave filter device 1500 is formed. The surface acoustic wave filter device 1500 includes first and second surface acoustic wave filters 1501 and 1513 in which the impedance at one end is four times the impedance at the other end.
The phase of first surface acoustic wave filter 1501 differs from the phase of second surface acoustic wave filter 1513 by 180 degrees. The first surface acoustic wave filters 1501 are arranged on both sides of the center IDT of a virtual longitudinally coupled resonator type surface acoustic wave filter having three IDTs designed to have substantially equal input and output impedances. IDTs are connected in series. That is, although the IDTs 1503 to 1505 are arranged along the surface wave propagation direction, one ends of the IDTs 1503 and 1505 on both sides in the surface wave propagation direction are commonly connected. The other end of the IDT 1503 is connected to the ground potential, and the other end of the IDT 1505 is connected to the unbalanced signal terminal 1512. Therefore,
IDTs 1503 and 1505 are connected in series.

On the other hand, one end of the central IDT 1504 is connected to the ground potential, and the other end is connected to the first balanced signal terminal 1510. In addition, 1502 and 1506 are reflectors.
The second surface acoustic wave filter 1513 is configured similarly to the first surface acoustic wave filter 1501.
That is, one end of the central IDT 1516 is connected to the ground potential, and the other end is connected to the second balanced signal terminal 1522. One end of each of the IDTs 1515 and 1517 is connected, and the other end of the IDT 1517 is connected to the ground potential. The other end of the IDT 1515 is an unbalanced signal terminal 151
2 are connected. Therefore, IDT1515 and IDT
1517 are connected in series between the ground potential and the unbalanced signal terminal 1512. In addition, 1514, 151
8 is a reflector.

As described above, when the propagation direction of the surface acoustic wave is the direction of arrow X in FIG.
01, the IDT 15 existing in front of the surface wave propagation direction
05 is connected to the unbalanced signal terminal 1512 and the second
In the surface acoustic wave filter 1513, the IDT 1515 disposed on the starting point side in the surface acoustic wave propagation direction has an unbalanced signal terminal 1
512, whereby the phase of the first surface acoustic wave filter 1501 is different from the phase of the second surface acoustic wave filter 1513 by 180 degrees.

Therefore, also in this embodiment, one end of the first surface acoustic wave filter 1501 and one end of the second surface acoustic wave filter 1513 are connected in common, and the unbalanced signal terminal 1
512, and the central IDTs 1504, 1513 of the first and second surface acoustic wave filters 1501, 1513.
Since one end of 16 is connected to each of the first and second balanced signal terminals, a surface acoustic wave filter device having substantially equal input / output impedance and having a balance-unbalance conversion function is configured.

In this embodiment, as in the first and second embodiments, the first and second balanced signal terminals 1510 and 152 are also provided.
Parasitic capacitance applied to 2 becomes almost equal. Therefore, the first
As in the second embodiment, the degree of balance is increased, and the amount of attenuation outside the pass band is greatly improved.

Although the surface acoustic wave filter device 1500 shown in FIG. 14 uses the first and second 3IDT surface acoustic wave filters 1501 and 1513, as shown in FIG. Wave filter 1501A,
1513A may be used.

The surface acoustic wave filter device 1 shown in FIG.
In 500A, the IDTs 1503 and 1503 shown in FIG.
5 and the IDTs 1531, 1532, 1533, 15
The embodiment is the same as the embodiment shown in FIG. 14 except that 34 is arranged. As described above, the IDT in each longitudinally coupled resonator type surface acoustic wave filter in the third embodiment
Is not particularly limited.

As shown in FIG. 16, a four-element surface acoustic wave filter device using two first and second surface acoustic wave filters may be used. In the surface acoustic wave filter device 1500B shown in FIG.
The surface acoustic wave filters 1501 and 1501A and the two second surface acoustic wave filters 1513 and 1513A are connected to form a four-element surface acoustic wave filter device.

Similarly to the above-described first and second embodiments, also in the third embodiment, the first and second surface acoustic wave filters whose input / output impedance is four times the output / input impedance are used. In addition, each of the first and second surface acoustic wave filters in which the phase of the second surface acoustic wave filter is 180 degrees different from the phase of the first surface acoustic wave filter is 2 ^n-1 (where n Is an integer of 1 or more), and a total of 2 ⁿ surface acoustic wave filters can be used to constitute the surface acoustic wave filter device of the present invention. Similarly, the first and second balanced signal terminals Can be reduced, and the attenuation outside the pass band can be increased.

In the first to third embodiments, 40 ± 5 degrees Yc
Although the utX-propagating LiTaO ₃ substrate was used, the present invention is not limited to such a piezoelectric substrate, and for example, a 64-degree to 72-degree YcutX-propagating LiNbO ₃ substrate or a 41-degree Yc
outX propagating LiNbO ₃ substrate or the like can be used,
Similar effects can be obtained.

FIG. 17 is a schematic block diagram for explaining a communication device 160 using the surface acoustic wave device according to the present invention. In FIG. 17, a duplexer 162 is connected to an antenna 161. A switch SW is provided between the duplexer 162 and the receiving mixers 163 and 163a.
, A surface acoustic wave filter 164 constituting an RF stage, and amplifiers 165 and 165a. Further, the surface acoustic wave filters 16 of the IF stage are added to the mixers 163 and 163a.
9, 169a are connected. Duplexer 1
An amplifier 167 and a surface acoustic wave filter 168 constituting an RF stage are connected between the mixer 62 and the mixer 166 on the transmission side.

As the surface acoustic wave filter 164 in the communication device 160, a surface acoustic wave device configured according to the present invention can be suitably used.

[0076]

According to the surface acoustic wave filter device of the present invention, the first and second surface acoustic wave filters whose input / output impedance is four times as large as the output / input impedance are provided. The phase of the filter is different from the phase of the first surface acoustic wave filter by 180 degrees;
^n-1 first and second surface acoustic wave filters are connected between the unbalanced signal terminal and the first balanced signal terminal and between the unbalanced signal terminal and the second balanced signal terminal, respectively. Have been. Therefore, the difference between the parasitic capacitances applied to the first and second balanced signal terminals is reduced, thereby improving the degree of balance. Therefore, in a surface acoustic wave filter device having a balanced-unbalanced conversion function and having almost the same input / output impedance, it is possible to greatly increase the attenuation outside the pass band.

[Brief description of the drawings]

FIG. 1 is a schematic plan view illustrating a surface acoustic wave filter device according to a first embodiment of the present invention.

FIG. 2 is a schematic plan view for explaining a conventional surface acoustic wave filter device prepared for comparison.

FIG. 3 is a diagram showing a comparison of the amplitude balance between the first embodiment and a conventional example.

FIG. 4 is a diagram showing a comparison of the degree of phase balance between the first embodiment and a conventional example.

FIG. 5 is a diagram illustrating attenuation frequency characteristics of the surface acoustic wave filter devices according to the first embodiment and the conventional example.

FIG. 6 is a schematic plan view for explaining a modified example of the surface acoustic wave filter device according to the first embodiment.

FIG. 7 is a schematic plan view showing another modified example of the surface acoustic wave filter device according to the first embodiment.

FIG. 8 is a schematic plan view showing still another modified example of the surface acoustic wave filter device according to the first embodiment.

FIG. 9 is a schematic plan view for explaining a surface acoustic wave filter device according to a second embodiment.

FIG. 10 is a schematic plan view showing a modification of the surface acoustic wave filter device according to the second embodiment.

FIG. 11 is a diagram showing a comparison of the amplitude balance between the surface acoustic wave filter devices of the second embodiment and the conventional example.

FIG. 12 is a diagram showing a comparison of the degree of phase balance between the surface acoustic wave filter devices of the second embodiment and the conventional example.

FIG. 13 is a diagram illustrating attenuation frequency characteristics of the surface acoustic wave filter devices according to the second embodiment and the conventional example.

FIG. 14 is a schematic plan view of a surface acoustic wave filter device according to a third embodiment.

FIG. 15 is a schematic plan view showing a modification of the surface acoustic wave filter device according to the third embodiment.

FIG. 16 is a schematic plan view showing another modification of the surface acoustic wave filter device according to the third embodiment.

FIG. 17 is a block diagram showing a schematic structure of a communication device including the surface acoustic wave filter of the present invention.

FIG. 18 is a schematic plan view showing a conventional surface acoustic wave filter device having a balance-unbalance conversion function.

[Explanation of symbols]

160 communication device 164 surface acoustic wave filter 200 surface acoustic wave filter device 201, 201A, 201B first surface acoustic wave filter 203 to 205 IDT 203A, 203B, 205A, 205B first and second
IDT section 212 ... first balanced signal terminals 216, 216A, 216B ... second surface acoustic wave filters 219, 220, 221 ... IDT 219A, 219B, 221A, 221B ... first and second
IDT unit 227: second balanced signal terminal 231: unbalanced signal terminal 251 to 254: IDT 701, 703: first surface acoustic wave filter 702, 704: second surface acoustic wave filter 705: unbalanced signal terminal 706, 707: first and second balanced signal terminals 800: surface acoustic wave filter device 801, 803: first surface acoustic wave filter 802, 804: second surface acoustic wave filter 1100: surface acoustic wave filter device 1101 ... first surface acoustic wave filters 1103, 1104, 1105 ... IDTs 1104A and 1104B ... first and second IDT units 1114 ... first balanced signal terminals 1115 ... second surface acoustic wave filters 1117, 1118, 1119 ... IDTs 1118A, 1118B: first and second IDT units 1128: second balanced signal terminals 11 9: Unbalanced signal terminal 1500: Surface acoustic wave filter device 1501: First surface acoustic wave filter 1503-1505: IDT 1510: First balanced signal terminal 1512: Unbalanced signal terminal 1513: Second surface acoustic wave filter 1515 to 1517 IDT 1522 second balanced signal terminal

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Hiroki Watanabe 2-26-10 Tenjin, Nagaokakyo-shi, Kyoto Inside Murata Manufacturing Co., Ltd. (72) Yuichi Takamine 2-26-10 Tenjin, Nagaokakyo-shi, Kyoto Stock Company Murata Manufacturing Co., Ltd.

Claims (15)

[Claims] 1. A surface acoustic wave filter device comprising an unbalanced signal terminal, first and second balanced signal terminals, and having substantially equal input and output impedances, wherein the unbalanced signal terminal and the first balanced 2 ^n-1 (where n is an integer of 1 or more) first surface acoustic wave filters which are connected between the signal terminal and one of the input and output impedances is about four times the other, and The first surface acoustic wave filter, which is connected between an unbalanced signal terminal and the second balanced signal terminal and has one of input and output impedances approximately four times that of the other, has a phase of 1
A surface acoustic wave filter device comprising: 2 ^n-1 (n is an integer of 1 or more) second surface acoustic wave filters different by 80 degrees. 2. The method according to claim 1, wherein the first and second surface acoustic wave filters are arranged along a surface acoustic wave propagation direction.
The first and second IDTs each having the above IDT, and at least one of the IDTs is divided into two in the cross width direction.
2. The surface acoustic wave filter device according to claim 1, wherein the first and second IDT units are connected in series. 3. 3. The virtual surface acoustic wave filter according to claim 1, wherein the first and second surface acoustic wave filters are configured such that input and output impedances are substantially equal.
IDT is divided into two in the cross width direction, and the first and second IDTs are divided.
The surface acoustic wave filter device according to claim 1, wherein the surface acoustic wave filter device has a structure in which a T portion is configured. 4. The surface acoustic wave filter device according to claim 3, wherein the virtual surface acoustic wave filter is a longitudinally coupled resonator type surface acoustic wave filter. 5. The longitudinally coupled resonator type surface acoustic wave filter has three IDTs arranged in a propagation direction of a surface acoustic wave, and a central IDT or IDTs on both sides are divided into two in an intersecting width direction to form the second IDT. The surface acoustic wave filter device according to claim 4, wherein the first and second IDT units are configured. 6. The first and second surface acoustic wave filters have one or two or more IDTs, and at least one IDT is divided into two in a surface wave propagation direction. The surface acoustic wave filter device according to claim 1, comprising two IDT units. 7. A virtual surface acoustic wave filter wherein the first and second surface acoustic wave filters are configured such that input and output impedances are substantially equal to each other. At least one IDT is divided into two in a surface wave propagation direction. The surface acoustic wave filter device according to claim 6, wherein the surface acoustic wave filter device is configured by: 8. The surface acoustic wave filter device according to claim 7, wherein the virtual surface acoustic wave filter is a longitudinally coupled resonator type surface acoustic wave filter. 9. The surface acoustic wave filter according to claim 8, wherein the longitudinally coupled resonator type surface acoustic wave filter has three IDTs, and a central IDT is divided into two in a surface wave propagation direction. apparatus. 10. The surface acoustic wave filter device according to claim 2, wherein one of the first and second IDT units is connected to a ground potential. 11. The surface acoustic wave device according to claim 1, wherein the first and second surface acoustic wave filters have a structure in which at least two IDTs are connected in series in a surface acoustic wave filter having a plurality of IDTs. Wave filter device. 12. The surface acoustic wave filter according to claim 11, wherein the first and second surface acoustic wave filters have a structure in which at least two IDTs are connected in series in a virtual surface acoustic wave filter having substantially the same input / output impedance. Surface acoustic wave filter device. 13. The surface acoustic wave filter device according to claim 12, wherein the virtual surface acoustic wave filter is a longitudinally coupled resonator type surface acoustic wave filter. 14. The longitudinally coupled resonator type surface acoustic wave filter has three IDTs, and IDs on both sides in a surface wave propagation direction.
The surface acoustic wave filter device according to claim 13, wherein T is connected in series. 15. A communication device comprising the surface acoustic wave filter device according to claim 1 as a bandpass filter.